The invention relates to flowmeters, and in particular, to methods and systems for determining a proportion of a majority component relative to a fluid flowing through a Coriolis flowmeter.
When a fluid that is being delivered through a pipline is measured, the amount of the fluid delivered is measured in terms of volumetric flow. The term xe2x80x9cfluidxe2x80x9d refers to any material in a liquid or solid state that flows. The volumetric flow rate is used to bill a customer for the amount of fluid delivered. A turbine, a positive displacement meter, or some other measurement system, measures the volume of the fluid as the fluid is delivered to the customer. The measurement system also measures the temperature of the fluid. The measurement system adjusts the volumetric measurement to a reference temperature. The customer is then billed based on the adjusted volumetric measurement.
Many fluids are sold based on standard conditions, which means that the measurement system assumes that the fluid being sold is pure. However, the fluid may be comprised of more than one component. A majority component represents a pure fluid that is being measured, such as the fluid being sold. The minority components represent impurities mixed in with the majority component.
For example, propane that is delivered to customers can be mixed with other components such as ethane, methane, etc. The ethane and methane are impurities that negatively affect the purity of the propane. A mixture of propane, ethane, and methane includes a discrete propane component, a discrete ethane component, and a discrete methane component. Unfortunately, turbines and positive displacement meters cannot effectively determine the proportion of the majority component relative to the fluid being delivered to a customer. Consequently, the customers are billed as if the fluid is pure.
One way to measure a mass flow of a fluid is with a Coriolis-effect mass flowmeter. Coriolis flowmeters measure mass flow and other information for fluids flowing through a flow tube in the flowmeter. Exemplary Coriolis flowmeters are disclosed in U.S. Pat. No. 4,109,524 of Aug. 29, 1978, U.S. Pat. No. 4,491,025 of Jan. 1, 1985, and Re. 31,450 of Feb. 11, 1982, all to J. E. Smith et al. Flowmeters are comprised of one or more flow tubes of a straight or curved configuration. Each flow tube configuration in a Coriolis flowmeter has a set of natural modes of vibration, which may be of a simple bending, twisting, torsional or coupled type. Each flow tube is driven to oscillate at a resonance in one of these natural modes of vibration. Fluid flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter. The fluid is directed through the flow tube(s), and exits the flowmeter through the outlet side of the flowmeter. The natural vibration modes of the vibrating, fluid-filled system are defined in part by the combined mass of the flow tubes and the mass of the fluid flowing through the flow tubes.
As fluid begins to flow, Coriolis forces cause points along the flow tubes to have a different phase. The phase on the inlet side of the flow tube commonly lags the driver while the phase on the outlet side of the flow tube leads the driver. Pickoffs are affixed to the flow tube(s) to measure the motion of the flow tube(s) and generate pickoff signals that are representative of the motion of the flow tube(s).
Meter electronics or any other ancillary electronics or circuitry connected to the flowmeter receive the pickoff signals. The meter electronics processes the pickoff signals to determine the phase difference between the pickoff signals. The phase difference between two pickoff signals is proportional to the mass flow rate of fluid through the flow tube(s). Therefore, the meter electronics can determine the mass flow rate of a fluid flowing through the flowmeter based on the pickoff signals.
An important component of Coriolis flowmeters and of vibrating tube densitometers is the drive or excitation system. The drive system operates to apply a periodic physical force to the flow tube, which causes the flow tube to oscillate. The drive system includes a driver mechanism mounted to the flow tube(s) of the flowmeter. The drive system also includes a drive circuit that generates a drive signal to operate the driver mechanism. The driver mechanism typically contains one of many well known arrangements, such as a magnet mounted to one flow tube and a wire coil mounted to the other flow tube in an opposing relationship to the magnet.
A drive circuit continuously applies a periodic driver voltage to the driver mechanism. The drive voltage is typically sinusoidally or square shaped. In a typical magnetic-coil drive mechanism, the periodic drive voltage causes the coil to produce a continuous alternating magnetic field. The alternating magnetic field of the coil and the constant magnetic field produced by the magnet force the flow tube(s) to vibrate in a sinusoidal pattern. Those skilled in the art will appreciate that any device capable of converting an electrical signal to mechanical force is suitable for application as a driver mechanism (See, U.S. Pat. No. 4,777,833 issued to Carpenter and assigned on its face to Micro Motion, Inc.). Also, the driver signal is not limited to a sinusoidal signal, but may be any periodic signal (See, U.S. Pat. No. 5,009,109 issued to Kalotay et. al. and assigned on its face to Micro Motion, Inc.).
As stated above, the meter electronics determines the mass flow rate of a fluid flowing through the flowmeter. The meter electronics also infers the density of the fluid based on the pickoff signals. Any density variations that are different than the known, reference densities are assumed to be due to temperature and not due to the purity of the fluid. Based on the measured mass flow rate and the inferred density of the fluid, the meter electronics determines the volumetric flow rate of the fluid flowing through the flowmeter. Unfortunately, current Coriolis flowmeters have not been effectively adapted to measure the proportion of a majority component relative to the fluid. Customers may therefore be billed for less than pure fluids.
The invention helps to solve the above problems, and an advance in the art is made, by systems, methods, and software configured to determine a proportion of a majority component relative to a fluid flowing through a Coriolis flowmeter. The invention advantageously provides a more accurate measurement of the amount, purity, and quality of a fluid being delivered. The invention also allows customers to be more accurately billed for fluids being purchased.
In one example of the invention, circuitry is configured to communicate with a Coriolis flowmeter to implement the invention. The circuitry comprises an interface means configured to receive pickoff signals and a temperature signal from the Coriolis flowmeter responsive to a fluid flowing through the Coriolis flowmeter. The fluid comprises a majority component. The interface means is also configured to transfer the pickoff signals and temperature signal to the processing means. The processing means is configured to process the pickoff signals and the temperature signal to determine a proportion of the majority component relative to the fluid.
In another example of the invention, the circuitry executes the following process to determine the proportion of the majority component. To start, the circuitry processes the pickoff signals to determine a mass flow rate of the fluid. The circuitry then divides the mass flow rate by a reference density of the majority component to yield a first volumetric flow rate. The reference density represents the density of the majority component at a reference temperature. The circuitry then processes the pickoff signals to determine a measured volumetric flow rate of the fluid flowing through the Coriolis flowmeter. The circuitry then determines a temperature-varying density. The circuitry multiplies the measured volumetric flow rate by the temperature-varying density to yield a product. The circuitry then divides the product by the reference density to yield a second volumetric flow rate. If the first volumetric flow rate equals the second volumetric flow rate, then the fluid is substantially pure. If the first volumetric flow rate does not equal the second volumetric flow rate, then the fluid is comprised of one or more minority components in addition to the majority component.
In another example of the invention, the circuitry executes the following process to determine the proportion of the majority component. To start, the circuitry processes the pickoff signals to determine a measured density of the fluid. The circuitry then processes the temperature signal to determine a temperature of the fluid. The circuitry determines a temperature-varying density based on the temperature. If the measured density equals the temperature-varying density, then the fluid is substantially pure. If the measured density does not equal the temperature-varying density, then the fluid is comprised of one or more minority components in addition to the majority component.